1. Field of the Invention
This invention relates to a propylene having a high melt-tensile strength. More particularly, it relates to a polypropylene having a high melt-tensile strength and crystallization temperature, having a superior stiffness and moldability, and capable of being remelted and used in a recycle manner after used as a molded product, a process for producing the polypropylene and a molded product therefrom.
2. Description of the Related Art
Crystalline polypropylene is superior in the mechanical properties, chemical resistance, etc. and very useful in the aspect of the balance between these properties and economy; hence it has been broadly used in various molding fields. However, since it has a low melt-tensile strength and a low crystallization temperature, it is inferior in moldability at the time of blow molding, foam molding, extrusion molding, etc.
As a method for elevating the melt-tensile strength and the crystallization temperature of crystalline polypropylene, a method of reacting an organic peroxide and a crosslinking agent with crystalline polypropylene in molten state is disclosed (Japanese patent application laid-open Nos. Sho 59-93711 and Sho 61-152754), but since a crosslinking agent is used, there has been raised a problem that odor remains in the resulting modified polypropylene. Further, improvement in the melt-tensile strength is insufficient; thus if the quantities of the organic peroxide and the crosslinking agent added are increased in order to elevate the melt-tensile strength, gel is formed; hence the moldability has been deteriorated and further, it has been impossible to remelt the polypropylene and use it in a recycle manner.
On the other hand, Japanese patent application laid-open No. Hei 2-298536 discloses that a method of reacting a peroxide of a low decomposition temperature with a semicrystalline polypropylene in the absence of oxygen, to thereby obtain a polypropylene having a free end, long chain branch and containing no gel. However, the improvement in the melt-tensile strength of the resulting polypropylene has been insufficient.
(Problems to be Solved by the Invention)
As described above, the polypropylenes obtained according to the methods of known inventions have raised such problems that it is insufficient in the improvements of the melt-tensile strength and the crystallization temperature, and besides since it has odor or contains gels; hence it is impossible to remelt and use it in a recycle manner.
The present inventors have made extensive research in a polypropylene having solved the problems of the above known inventions and suitable to blow molding, foam molding, extrusion molding, etc., and a process for producing the same, and as a result, have found that when a specified organic peroxide is reacted with a polypropylene under specified conditions, followed by melt-kneading, then a polypropylene having a high melt-tensile strength is obtained and when this polypropylene is used as a molded product, the problems of the prior inventions can be solved, and the first and second inventions of the present application have been completed.
The present inventors have made further research, and as a result, have found that when a polypropylene composition containing a polypropylene having a high viscosity in a specified quantity is used, the melt-tensile strength is further notably improved. Based upon this knowledge, the third invention has been completed.
As apparent from the foregoing, the object of the present inventions is to provide a polypropylene having a high melt-tensile strength and crystallization temperature and also having a superior stiffness and moldability, and yet being capable of remelting the polypropylene after used as a molded product and using it in a recycle manner; a process for producing the polypropylene; and a molded product from the polypropylene.